Oven



June 28, 1966 M. F. MOONEY OVEN Filed NOV. 12, 1963 Fig. 3.

Fig. 4.

INVENTOR. Merrick F. Mooney BY W.WJ\

ATTORNEY United States Patent Filed Nov. 12, 1963, Ser. No. 323,000 8 Claims. (Cl. 219-1055) This invention relates to heating of materials by exposure to electromagnetic radiation and concerns especially distribution of microwave energy for uniform heating thereby in an oven or similar enclosure.

Increase in temperature of materials exposed to electromagnetic radiation in the microwave portion of the spectrum (from about one thousand to three hundred thousand megacycles per second, corresponding to wavelengths of from about thirty centimeters to one millimeter) is a familiar phenomenon. Microwave generators operating in the midportion of this range are used to provide energy to cooking ovens or the like. However, the pattern of radiation established in an oven, for example, resembles standing waves to such an extent that the food or other material to be heated is affected nonuniformly. For this it is customary to stir the pattern or mix the modes by means of a rotating fan having electrically conductive blades to reflect the radiation intermittently. However, the added initial cost and upkeep of such a device are unwelcome, and there is a great need for improvement.

A primary object of the present invention is assurance of heating uniformity in a microwave oven or the like without use of moving blades therein.

Another object is coupling of microwave energy froma waveguide into an oven or similar enclosure by stationary means effective to smooth or even out the energy pattern therein.

A further object is accomplishment of the previous objects without significantly decreasing the useful volume of the oven or like enclosure.

Other objects of this invention, together with means and methods for attaining the various objects, will be apparent from the following description and the accompanying diagrams.

FIG. 1 is a partially diagrammatic sectional side elevation of microwave oven apparatus embodying the present invention;

FIG. 2 is a plan view of a portion of the apparatus of FIG. 1 taken at IIII thereon;

FIG. 3 is a diagrammatic view of certain electromagnetic components partly shown in the previous views;

FIG. 4 is a partially diagrammatic perspective view of a component form of a particle useful in the practice of this invention;

FIG. 5 is a view similar to FIG. 4 of another component form of such particle; and

- FIG. 6 is a fragmentary cross-sectional view through a surface portion of a particle so useful.

In general, the objects of the present invention are accomplished, in apparatus for heating materials with microwave energy in an enclosure supplied therewith from an external source along a path therebetween, by means of a group of particles in the path adapted to be preferentially oriented upon application of an external magnetic field thereto and adapted to reflect incident microwave energy, means for applying an external magnetic field to the particles and thereby preferentially orienting them, and means for changing the direction of the applied field and thereby reorienting the particles and varying the direction of reflection of microwave energy incident thereon.

FIG. 1 shows an oven enclosure 11 having a door 12 in the front wall and having a magnetron or other ice microwave generator 13 interconnected to an opening or port 14 in the rear wall by a waveguide 15, which is oriented at about a forty-five degree angle thereto. Located at the junction of the waveguide 15 to the oven enclosure 11 at the lower side of the opening or port 14 is level portion 16, which supports a shallow layer or group of particles 20 in a similarly shallow container 21.

FIG. 2 shows in plan, viewed from above as indicated on FIG. 1, the container 21 of the particles 20, together with adjacent portions of the apparatus. A pair of aligned electromagnets 23, 24 and another pair 25, 26 are located adjacent the upper left and lower right and the upper right and lower left edge portions of the container 21. Electrical connections for these electromagnets and means for securing them in place are omitted from this view in the interest of clarity.

FIG. 3 shows diagrammatically the electrical connections omitted from the previous view, together with switching means 29, shown in block form, for actuating the respective pairs of electromagnets alternately by applying direct potential thereto. The switching means may comprise motor-driven mechanical switches or electronic components, such as a flip-flop device. The design and construction of suitable switching means being well within the knowledge and capability of persons having ordinary skill in the art, no further description or illustration thereof is included herein.

FIGS. 4 and 5 illustrate diagrammatically component forms (e.g., single crystals) of particles 20, which normally will comprise large numbers or aggregates of such component forms. Both views show cubic crystals in perspective, 34 in FIG. 4 and 35 in FIG. 5. The shading indicates in each a readily niagnetizable plane: surface plane 36 (characteristic of iron) in FIG. 4 and diagonal plane 37 (characteristic of nickel) in FIG. 5.

In practice, as shown in the fragmentary sectional view through the surface of one particle 20 in FIG. 6, the particles preferably will be coated with an electrically nonconducting lubricant 30. The lubricant may be liquid, such as a transformer oil, or solid, such as a polymeric halogenated hydrocarbon (e.g., polytetrafluoroethylene). The surfaces of the particles will be largely planar, and the lubricant facilitates reorientation of the particles upon switching of the respective pairs of electromagnets off and on to vary the direction of the applied magnetic field.

Operation of the illustrated and described apparatus is readily understandable. Microwave energy generated by magnetron 13 passes through waveguide 15 in to oven 11 through opening 14, and much or most of the energy is reflected from particles 20 at or near the junction of the waveguide with the oven. Application of a magnetic field by one pair of electromagnets orients many or most of the particles in a certain direction, and switching the applied direct potential to the other pair of electromagnets reorients the particles in another direction, corresponding to the right angle between the pairs of magnets, and alters the angle of reflection of the microwave energy incident thereon. The result is a mixing of the energy pattern in the oven and equalization of the temperature of lossy dielectric material, such as foodstuffs, heated by absorption of such energy therein.

The particles preferably are composed wholly or largely of ferromagnetic material, such as iron, nickel, cobalt, or alloys of those materials with one another or with other suitable materials. They may and preferably should exhibit substantial magnetic hardness or permanent magnetization, as is helpful in reorienting them upon application of an external magnetic field.

Although two pairs of electromagnets have been illustrated, both in essentially the plane of the layer of particles 20, it should be understood that other means for imposing an external magnetic field and for changing the direction thereof may be added thereto or substituted therefor and that the location or positioning of the illustrated or other such means may be altered as may be indicated to obtain best results with various types of particles. It will be apparent that the reorientation of the reflective surface of the particles resulting upon changing the direction of the magnetic field should alter the angle of incidence of microwave energy thereon and thereby vary the angle of reflection therefrom especially into the oven.

In practice, particles seldom or never exactly duplicate on a macro scale the form of single-crystal components (elg., because of irregularity of surface and varied orientation of components) so that the desired effect is obtainable to some extent under nearly all placement conditions so long as the applied field is effective to reorient the particles at all.

Other modifications in the construction or arrangement of the apparatus of this invention may be made while retaining the benefits and advantages thereof, some of which have been pointed out above and others of which will become apparent to those undertaking to practice the invention.

I claim as my invention:

1. lln apparatus for heating materials with microwave energy in an enclosure supplied therewith from an external source along a path therebetween, a group of particles in the path adapted to be preferentially oriented upon application of an external magnetic field thereto and adapted to reflect incident microwave energy, means for applying an external magnetic field to the particles and thereby preferentially orienting them, and means for changing the direction of the applied field and thereby reorienting the particles and varying the direction of reflection of microwave energy incident thereon.

2. In apparatus for heating materials with microwave energy in an enclosure supplied therewith from an external source along a path therebetween, a group of particles in the path adapted to be preferentially oriented upon application of an external magnetic field thereto and adapted to reflect incident microwave energy, a plurality of means for applying an external magnetic field to the particles and thereby preferentially orienting them in a plurality of directions, one direction at a time, and means for actuating the field-applying means sequentially and thereby reorienting the particles and varying the direction of reflection of microwave energy incident thereon.

3. In apparatus for heating materials with microwave energy in an enclosure supplied therewith from an external source along a path therebetween, a group of particles in the path adapted to be preferentially oriented upon application of an external magnetic field thereto and adapted to reflect incident microwave energy, means for applying an external magnetic field to the particles and thereby preferentially orienting them in one direction, additionalmeans for applying an external magnetic field to the particles and thereby preferentially orienting them in another direction, and means for actuating the fieldapplying means sequentially at a frequency low with respect to the microwave frequency, and thereby reorienting the particles and varying the. direction of reflection of microwave energy incident thereon.

4. In apparatus for heating materials with microwave energy in an enclosure supplied therewith from an external source along a path therebetween, a group of particles in the path adapted to be preferentially oriented upon application of an external magnetic field thereto and adapted to reflect incident microwave energy, means for applying an external magnetic field to the particles and thereby preferentially orienting them in one direction, additional means for applying an external magnetic field to the particles and thereby preferentially orienting them in another direction, and means for actuating the fieldapplying means sequentially at a frequency low with respect to the microwave frequency, and thereby reorienting the particles and varying the direction of reflection of microwave energy incident thereon, the direction of reflection at least part of the time being into the enclosure and adapted to modify the microwave energy pattern therein.

5. In a microwave oven having an external source of microwave energy, means joining the external source to the oven for conducting microwave energy therebetween, a layer of particles individually characterized by a plane of preferential magnetization and a planar surface adapted to reflect microwave energy, being located in the energy path in the vicinity of the junction and orientable in a plurality of directions dependent upon direction of an external magnetic field applied thereto, and means for applying a magnetic field to the particles sequentially in a plurality of directions to orient them in a plurality of successive directions and thereby vary the direction of reflection of microwave energy incident on the particles.

6. In a microwave oven having an external source of microwave energy, means joining the external source to the oven, a layer of ferromagnetic particles having planar surfaces located in the energy path in the vicinity of the junction and orientable in a plurality of directions dependent upon the direction of an external magnetic field applied thereto, and means for applying a magnetic field to the particles sequentially in a plurality of directions to orient them in a plurality of successive directions and thereby vary the direction of reflection of microwave energy incident on the particles.

7. In a microwave oven having an external source of microwave energy, means joining the external source to the oven for conducting microwave energy therebetween, a layer of particles individually characterized by a plane of preferential magnetization and a planar surfce adapted to reflect micro-wave energy, being located in the energy path in the vicinity of the junction and orientable in a plurality of directions dependent upon the direction of an external magnetic field applied thereto, an electrically nonconductive lubricant coating the particles, and means for applying a magnetic field to the particles sequentially in a plurality of directions to orient then in a plurality of successive directions and thereby vary the direction of reflection of microwave energy incident on the particles.

8. In a microwave oven having an external source of microwave energy, means joining the external source to the oven for conducting microwave energy therebetween, and including a waveguide having a reflective angled portion thereof oriented substantially level and supporting thereon a layer of particles individually characterized by a plane of preferential magnetization and a planar surface adapted to reflect microwave energy, the particles being orienta-ble in a plurality of directions dependent upon the direction of an external magnetic field applied thereto, and means for applying a magnetic field to the particles sequentially in a plurality of directions to orient them in a plurality of successive directions and thereby vary the direct-ion of reflection of microwave energy incident on the particles.

References Cited by the Examiner UNITED STATES PATENTS 2,790,054 4/1957 Haagensen 21910.55 2,921,308 1/1960 Hansen et al. 343787 2,973,916 2/1961 Medved 343787 12,992,425 7/1961 Pratt 343- 1 8 2,992,426 7/1961 Borcherdt 3431 8 RICHARD M. WOOD, Primary Examiner.

L. H. BENDER, Assistant Examiner. 

1. IN APPARATUS FOR HEATING MATERIALS WITH MICROWAVE ENERGY IN AN ENCLOSURE SUPPLIED THEREWITH FROM AN EXTERNAL SOURCE ALONG A PATH THEREBETWEEN, A GROUP OF PARTICLES IN THE PATH ADAPTED TO BE PREFERENTIALLY ORIENTED UPON APPLICATION OF AN EXTERNAL MAGNETIC FIELD THERETO AND ADAPTED TO REFLECT INCIDENT MICROWAVE ENERGY, MEANS FOR APPLYING AN EXTERNAL MAGNETIC FIELD TO THE PARTICES AND THEREBY PREFERENTIALLY ORIENTING THEM, AND MEANS FOR CHANGING THE DIRECTION OF THE APPLIED FIELD AND THEREBY REORIENTING THE PARTICLES AND VARYING THE DIRECTION OF REFLECTION OF MICROWAVE ENERGY INCIDENT THEREON. 